Radio receiving system



July 6, 1937.. R. M. SMITH RADIO RECEIVING SYST EM Filed June 30, 1933 2Sheets-Sheet-l /.s flTTOEl/EX 'July 6, 1937. R. M. SMITH RADIO RECEIVINGSYSTEM 2 Shets-Sheet 2 Filed June 50, 1935 smtk Patented, July 6, 1937UNlTED STATES PATENT- OFFICE to Radio Corporation of America, acorporation of Delaware Application June 30, 1933, Serial No. 678,410

I I 23 Claims.

The present invention relates to radio receiving systems, and moreparticularly, to radio receiving systems wherein one or more electricdischarge devices or electronic tubes are caused to function in aplurality of signal conveying circuits. Such systems are of. increasingcommercial importance in connection with midget radio receivers,automobile receivers and the like, wherein certain definite requirementsin regard to size, current consumption and cost must be met.

In automobile receivers, in particular, it is important that currentconsumption be kept at minimum value while at the same time maintaininga high level of sensitivity. Accordingly, it

is desirable to reduce the number of current consuming devices, and inparticular, the number of tubes employed in such apparatus withoutcorrespondingly reducing the operating efficiency.

To this end, a single electric discharge device or vacuum tube may bearranged to function as an element of a plurality of signal conveyingcircuits.

Radio receiving circuits and the like, wherein an electronic tubeperforms two functions, as in a refiexed amplifier, are known, as wellas circuits wherein further functions are provided, though attendedoften by undesirable complicaticn of said circuits or of the circuitarrangement. It is conceivable, however, that if a further combinationof functions may be given to one vacuum tube, without introducingundesirable circuit complications, the number of tubes necessary for usein a given receiving circuit may be greatly reduced and to goodadvantage.

It is, therefore, an object of the present invention to provide animproved receiving system embodying a single electric dischargeamplifier device wherein a reduction in operating current is efiectedwith increased amplification and wherein said device performs aplurality of functions in separate signal circuits thereof.

It is a further object of the present invention merits, namely acathode, a control grid, an

anode, and screen and suppressor grids, whereby a greater amplificationis obtainable therefrom and, in addition, at least .one and preferablytwo 5 anodes or plates also associated with the cathode,

independently of the other electrodes, for diode rectification of signalcurrents.

' It is a still further object of the present invene tion to provide aradio receiving system wherein, in a single tube amplifier device of thecharacter above described, the combined functions. of high frequencyamplification, detection, low frequency amplification, and automaticvolume control may be provided through simple circuit means.

In this connection, the present invention is,

therefore, particularly adapted for use with.

superheterodyne type receivers to provide a combfned intermediatefrequency amplifier-second detector-automatic volume control-audiofrequency amplifier system, the vacuum tube amplifierdevicepreferablybeing of the pentode type. Such a device provides, in anamplifier, a rela-' tively high amplification factor withcorrespondingly low operating potentials and a stable operatingcharacteristic. The use of such a device and circuit in a battery orautomobile receiver results in high gain with an appreciable reductionin the current consumption and battery drain.

The invention, however, is not limited to superheterodyne receivers ofthe battery type, nor to a second detector circuit of a superheterodynereceiver, but may be applied to any detector circuit which is associatedwith and interposed between high frequency and low frequency amplifiercircuits and in conjunction with automatic Volume or gain control meansfor the system in which the detector is located.

The use of a separate and additional diode plate for supplying controlpotentials or current to other circuits, such as automatic volumecontrol circuits, may be desirable in certain receiving systems, andaccordingly, it is a further object of the present invention to providean improved circuit of the character above described, wherein a dioderectifier function and an automatic volume control function areseparated.

It is a still further object of the present inven- In accordance withone embodiment of the invention, a diode detector is supplied withsignal energy from the anode or output'circuit of a pentode typeamplifier, both the detector and amplifier beingjprovided in a singleenvelope and having "a common cathode, and the audio fre quency signaloutput, therefrom is reflexed, by, resistance or impedance coupling, forexample,'

preferably onto the pentode grid then back through the pentode, and thepentode output circuit, to the utilization system or to a furtheramplifier, whereby both the control grid and the anode of the pentodeserveto carry both high and low frequency signals, suitably filteredinput and the detector circuit or indirectly from a separate rectifiercircuit in connection with a separate anode, whereby as hereinbeforestated, the device is provided preferably with two diode plates.

The invention will, however, be better understood from the followingdescription when taken in connection with the accompanying drawings, andits scope will be pointed out in the appended claims.

In the drawings, Fig. 1 is a schematic circuit diagram of a radioreceiving system embodying the invention; and

Figs. 2, 3 and 4 are similar diagrams of modifications of the systemshown in Fig. 1.

Referring to Fig. 1, a high frequency amplifier 5 and a low frequencyamplifier 6 having an output device 1 provide the usual signal channelof a receiver, with a detector circuit or system 8 therebetween havingaplurality of functions in accordance with the invention, and ashereinbefore pointed out.

In the present example, a superheterodyne type of receiver is indicated,wherein a radio frequency amplifier device 9 and a combined detector andoscillator device I6 are provided in the high frequency amplifier 5 andconnected in customary cascade relation through suitable couplingcircuits I I between a high frequency input or antenna circuit I2 and ahigh frequency output circuit I3.

This apparatus is preferably electrically shielded as indicated by thedotted rectangle enclosure therefor, having a ground lead or baseindicated at I4. The ground lead may not necessarily be connected toground, but represents the low potential lead or circuit connection ofthe apparatus. 'A cathode return lead I5 for the two devices 9 and II isconnected to the ground lead I4 as indicated, and includes a self biasresistor I6. Additional biasing potentials for volume control purposesare supplied to the devices 9 and I0 through a supply lead indicated at11. This lead includes a high frequency filter provided by suitableseries resistors I8 and bypass condensers I9. This circuit connectionwill further be described hereinafter.

An anode potential supply lead also for this portion of the receiver isindicated at 20. For the reason that the construction and circuitarrangement of this portion of the receiver does not concern the presentinvention, further description is believed to be unnecessary, and forthe sake of simplicity and clearness in the drawings, the remainer ofthe circuits have been omitted.

Likewisa'the audio frequency amplifier 6 represents any suitable lowfrequency amplifier having an electric discharge amplifier device orvacuum tube 2| connected between a suitable input circuit 22 and anoutput circuit 23 leading to the output device ,1. Audio or lowfrequency coupling transformers are indicated at 24 and 25 to provide acascade connection through the amplifier for signal potentials deliveredto the input circuit 22. Since the audio or low frequency amplifier andthe output device represent any suitable utilization means for the lowfrequency signals, and do not form part of the present invention,further illustration of the same and a further description are believedto be unnecessary. The amplifier is indicated as being enclosed in asuitable casing or container, by the dotted rectangle 6, and is providedwith suitable anode potential supply and return ground leads 26 and 21,respectively.

The high frequency output circuit I3, which may be taken as representingany source of high frequency modulated radio signals, is coupled to thecircuit 8, which, in turn, is coupled to the low frequency input circuit22 to complete the signal channel of the receiving system. The modulatedsignal current, in passing through the circuit 8 between the highfrequency signal output circuit I3 and the low frequency signal inputcircuit 22, is caused to pass through a plurality of transformations,including amplification at high frequency, diode detection,amplification at low frequency, and rectification for providing directcurrent control potentials for automatic volume control purposes.

In providing the several functions in this transformation, a singleelectric discharge or vacuum tube device 28 is utilized in the circuit8, such device having a single cathode 29, at least one diode plate oranode 30 and preferably at least one other anode electrode 31, a firstor inner grid 32, an output anode 33, a screen or second grid 34, andpreferably a third or suppressor grid 35, although such device mayfunction in the circuit of the present example without such suppressorgrid. With an indirectly heated cathode in a device as illustrated, aheater element 36 is also provided for the cathode. Such a device willbe termed a duplex diode pentode.

The cathode 29 is associated with the diode plates 30 and SI and alsowith the remaining pentode electrodes or elements 32 and 33. The screengrid 34 serves to decouple, in a well known manner, the last-namedtriode elements which serve as control grid and anode, respectively.

As will hereinafter be seen, a tube of this character provides theadvantage that the electron stream of a portion thereof which isutilized as an amplifier may be separated from the electron stream ofanother portion which provides a diode rectifier, both the amplifier andrectifier being within the same electric discharge device 28 and withthe common cathode, thereby permitting separation of the amplifiercircuits from the rectifier circuits.

The source of high frequency signal potentials, rep-resented by the highfrequency output circuit I3, is coupled to the control grid 32 through ahigh frequency input circuit 31. The input circuit includes a suitablehigh frequency input impedance or coupling device such as the tunedsecondary 38 of a coupling transformer 39. The grid receives a suitablebiasing potential through this circuit and through a low potentialsupply lead 40 therefor, connected to the ground lead I4 through acoupling resistor 4|. The biasing potential is supplied from anysuitable source such as a self bias resistor 42 in the cathode returnlead, indicated at 43. The self biasing resistor 42 is provided with asuitable radio frequency and audio frequency bypass condenser 44 alsoconnected with the ground lead I4. A suitable high frequency bypass. forthe circuit 31, directly to the cathode lead 43, is provided by acondenser 45.

The input circuit 31 is tuned to the frequency of the incoming signal,such as the selected intermediate frequency, and through it, theincoming sesame signal, usually an audio frequency modulated radiofrequency carrier wave, is applied to the control electrode 32. p

Intermediate frequency signals delivered to the control grid 32 from theinput circuit 3.1 are amplified and transmitted from the pentode outputanode circuit indicated at 46, through a coupling device 41 locatedtherein and a supply lead 48 to at least one, and preferably both, ofthe diode plates 30 and 3| in parallel as shown.

In the present example, the coupling device 41 is a high or intermediatefrequency transformer having a primary 49 in the amplifier outputcircuit 38 and a secondary 5|] connected to the lead 48 in the dioderectifier circuit. The low potential side of the primary is connected,to ground through a suitable high frequency bypass condenser 59, andalso, to the input circuit 22, through which it is connected to thepositive anode supply lead 25, as indicated in the drawings. The lastnamed lead is connected with a main high potential supply lead 52 whichis connected with a suitable current supply source,

The current supply unit 53 is energized from a a suitable power sourcesuch as a battery 54, in an automobile installation, although any othersuitable power source may be utilized with the proper supply means inthe unit 53. The battery and the power supply unit 53 connectedtherewith are grounded as indicated. While the present receiving systemshown in Fig. 1 relates particularly to automobile radio receivers, thesupply source and battery circuit do not form part of the invention and,therefore, are not believed to require further description.

The low potential side of the secondary 50 of the coupling device 4? isconnected, through a resistor 5'! having arelatively high resistancevalue, to the movable contact 58 of a potentiometer device or resistor59. The potentiometer device is connected between a lead 69 in turnconnected with the cathode lead 43 and the cathode, and a lead SI and acoupling condenser 62. The latter is connected with the lead 49 and thelow potential side of the input or grid circuit 31, between the latterand the coupling resistor ll. The leads 65 and ii are preferablyelectrically shielded, with the shield connected to ground as indicatedby the dotted lines 55' and 6!, for the reason that they are usuallyextended, in use, to a suitable control point for the device 59, in anautomobile installation.

From an inspection of the circuit diagram, it will be seen thatmodulated high frequency signals appearing in the output circuit 46 areamplified because of the high frequency impedance means ll in circuittherewith and are, through said device, transferred to the rectifiercircuit which includes the lead 58 and the diode plates 30 and 3|.tified in conjunctionwith the cathode 29 through the rectifier circuitwhich may be traced through the cathode lead 43, thence to the lead 60,through the resistor element 59 of the potentiometer device to themovable contact 58 and the lead',

63, and through the high resistance element 5'! The modulated signalsare then rec-' back to the low potential side of the. secondary 5B ofthe high frequency coupling device 41.

'The diode rectified signal current flowing in the circuit aboveoutlined comprises both an audio frequency'signal component and a directcurrent component and is applied to the .resistance elements in seriesto set up controlling potentials across the element 51 and any portionof element 59 which may be in circuit there-, with. The direct potentialis applied to the automatic volume control circuit ll through a supplylead 64 connected to the resistance element 5! at a suitable point suchas its negative end or terrninal adjacentgto the low potential side ofthe secondary 50. g

Because of the diode rectification, it will be seen that the resultingrectified current will flow in'the resistor 5'! in the direction of thearrow, whereby a negative potential is applied to the control circuitl'l' for the amplifier'ii in response to an applied carrier wave, anincrease in the intensity of the latter causing an increased negativecontrol potential to be applied tothe preceding amplifiers and acorresponding reduction in the gain therein. The potential drop causedby the flow of rectified signal current through the resistor 5! is thusapplied to the amplifier for automaticv volume control use and variesin.

response to changes in the carrier wave intensity.

Because of the nature of the amplifier devices used in modern radioapparatus, a' Wide range of control potentials is required, andtherefore, the voltage available across the rectifier circuit, includingthe, resistor 51, or between the supply lead 64 and the groundlead 14,may be'relatively high. For the above reason, the resistor 5'6 may havea relatively high value,'preferably several hundred thousand ohms, with.the type of tubes and circuit shown.

This resistor 5'! also serves the purpose of stepping down thecorresponding audio frequency signal potential to be applied at thecontact 58 in order not to overload the grid 32, with an adjustment ofthe contact 58 for maximum volume.

It will be seen that as the contact 58 is moved to the lower end of theresistor 59, as viewed in the drawings, the contact will be at cathodepotential, while as the contact is movedto positions approaching theextreme opposite position, the contact will be decoupled increasinglyfrom the cathode through the introduction of the resistor59 and willcorrespondingly increasingly be coupled to the control grid 32.

1 Audio or low frequency potentials set up across the resistor 59 areconveyed from said resistor through the lead 6!, the coupling condenser62 and the lead 58, to the grid 32 through the circuit 3? which is oflow impedance, to audio frequency signals. The impedance of the couplingresistor 45 is of such a value that it offers a relatively highimpedance to the audio frequency signal potentials.

Viewed in another aspect, operation of the audio frequency volumecontrol potentiometer,

gridof the pentode amplifier. The greater ,re-

sir ta nce causes a greater potential ,dropand,

therefore, a higher audio frequency potential on the control grid 32.

A suitable bypass condenser 65 is provided for the high frequencycircuit to ground from a point between the resistor 51 and the lowpotential end of the secondary 50. The screen grid 34 is also suppliedwith potentials through a supply resistor 66 in connection with thesupply lead 52, and the resistor is provided with a suitable bypasscapacitor 6'! for filtering purposes.

Audio frequency signals placed upon the control grid 32 are amplifiedand applied to the output anode circuit 45 and find a low impedance paththrough the high frequency coupling device 4'! to the input circuit 22for the audio frequency amplifier 6. The high frequency bypass condenser5! is of a value which does not offer any appreciable shunt effect foraudio frequencies upon the circuit. However, for tone control purposesit may be desirable to provide a bypass capacitor such as that indicatedat 68, and a controlling switch 69 in the anode output circuit 46between ground and the junction of the high and low frequency circuitimpedance elements, represented by the coupling elements 41 and 24 inthe present example, as indicated. Upon closure of the switch 69 certainhigher audio frequency signals may then be bypassed to ground andinterference from noise sources eliminated, prior to amplification inthe audio frequency amplifier.

The rectified signal current flows through fixed and variable voltagedivider resistors 53 and 59, respectively, in the rectifier outputcircuit, the first of which is utilized as an impedance for supplyingautomatic volume control potentials to preceding amplifier devices, at arelatively high value for the suppression of strong signals. Therectified audio frequency signal component is reduced through theresistor 51 to such a value that with a maximum incoming signal wave andwith the potentiometer volume control contact 58 at the maximum volumeposition at the upper end of the resistor 59, as viewed in the drawings,the control grid 32 may not then be overloaded appreciably by the audiofrequency signal, whereby noticeable distortion may be introduced.

In the present example, and as a preferred arrangement of the circuits,the high frequency signal input circuit 3? is connected with theinnermost or first grid of the amplifier device, which is the grid 32indicated in the drawings. While both of the anodes 3i) and 3! 'of thediode rectifier are connected together and utilized in parallel in thecommon rectifier circuit, they may, in certain applications, beconnected to a common signal input circuit and to separate outputcircuits for controlling difierent functions in the receiving system, aswill hereinafter be described.

The resistor 4! between the low potential side of the circuit and groundmay be relatively high, for example, such as one half megohm, as anaudio frequency coupling impedance, while the radio frequency bypasscondenser 45 may have a value of substantially 300 micro-micro-farads,being in shunt tothe grid circuit and therefore being of relatively hi himpedance to audio frequency signals as is desirable in order not toaffect appreciably the audio frequency characteristic of the signaltransmission. The resistor 42 is of suflicient value to provide thedesired bias potential on the grid 32, for example, 3 to 6 volts in apreferred device of the type shown, and the bypass capacitor orcondenser 44 may have a value of 5 microfarads.-

It should be noted that the devices 9 and I0 in the input signal circuitof the receiver receive a normal biasing potential from the fixed sourceprovided by the self bias resistor l6 and an additional signalcontrolled bias potential from the rectifier circuit through the supplylead 64, with the resistor 57 as the source.

With the diode rectifier circuit connected to the cathode and with aself bias resistor 42 in circuit with the cathode 29 of the combineddetector amplifier device 28, it will be seen that the potentialexisting in the self bias resistor 42 is applied to the biasing circuitsof the devices 9 and H] in opposition to the bias potential provided bythe source it. Accordingly, in the circuit shown, the source 16 isarranged to provide an additional potential equal to that provided bythe source 42, whereby a normal bias is obtained on the devices 9 andI0.

This may more readily be seen by tracing the bias circuit for the device9- from the input grid circuit thereof, through the circuit Ii, resistorI8, circuit lead l1, through the second filter resistor I8 to the leadE4, thence through the impedance or resistor 5'1, lead 63, the contact58, a portion of the volume control resistor 59, through the lead 69 tothe cathode lead 43. From this point, the circuit may further be tracedthrough the self bias resistor 42 to the ground lead (4,

thence through the resistor I 6, to the cathodes of the devices 9 andIll. The polarity of the potential existing in the various resistorsmentioned'is indicated by suitable polarity marks adjacent to theterminals thereof, and in tracing the circuit outlined, it will be seenthat a potential existing in the resistor I6 is, in the circuitoutlined, in opposition to that existing in the resistor 42.

.ttention is now directed to Fig. 2 wherein an electric dischargeamplifier and rectifier device 70, of the tetrode or screen grid type isprovided with an inner grid H connected with a high frequency signalinput circuit E2, the low potential side of which is represented by thegrid return lead 13.

The main anode is indicated at 8B and is connected with a high frequencyanode output circuit M, which is connected through a high frequencycoupling device '85 and a high frequency supply lead 16 with an anode llassociated with the cathode 78 to provide a diode rectifier. A screengrid 19 is provided between the main anode 89 and the control grid ll.

High or intermediate frequency signals, amplified in the tetrode portionof the device 18, are supplied through the output circuit 14 and thecoupling device to the input circuit 16 for the anode Tl. The signalsare rectified through the diode rectifier provided by the anode Ti andthe cathode l8, and pass through an audio frequency and direct currentimpedance element 8! in the form of a tapped resistor providing apotentiometer, the movable contact of which is indicated The rectifiercircuit is completed from the resistor 8| to the low potential side 33of the rectifier circuit, which includes the coupling device 15. Thismay be a suitable tuned high frequency input transformer as indicated.Any other suit-- able coupling device, however, may be used in theoutput anode circuit M for coupling the latter to the diode rectifiercircuit.

It will be noted that the rectifier or diode circuit returns directly tothe cathode 7S, whereby the only potentials existing in the rectifiercircuit are those caused by the rectification of signals, the signalpotentials being available across the impedance element BI. Thesepotentials are variably applied to the inner or control grid 'iI througha connection with the variable tap 92 which may be traced through acoupling con- 1 denser 86 and a combined coupling and high frequencyfilter impedance represented by a resistor element Bl between thecoupling condenser 89 and the ground lead indicated at 89.

The connection for the grid lead 73 is made at a suitable lowerpotential tap point 83 on the resistor 8'! whereby overloading of thegrid ii with audio frequency signals is prevented, when the tap 82 ismoved to the extreme audio frequency volume position at the right handend of the resistor 8!, as viewed in the drawings. A bypass condenser 84from the lead T9 to ground and cathode provides, with the resistor 8'5,a suitable high frequency filter for the audio frequency or dioderectifier circuit.

Suitable normal operating or biasing potential for the grid II issupplied through a portion of the resistor 81 from a self bias resistor99 in the cathode return lead 99.

This circuit is similar to that shown in Fig. 1, except that the audiofrequency potentials applied to the inner or control grid '7! areprevented from reaching excessively high values by a fixed ratioestablished by the tap 98 on the'impedance device 87. The audiofrequency volume control device is directly connected to the impedanceelement iii in the rectifier circuit, and suitable audio frequencypotentials for the desired volume are then selected directly therefrom,subject, however, to a fixed reduction ratio in the impedance 81. Highfrequency or intermediate frequency signals are supplied to the inputcircuit 12 through a suitable input coupling device 9!, and the audiofrequency output signals are transferred to the output circuit throughan audio frequency output device 92 in connection with the output anodecircuit M for the tetrcde, in the same manner as described in connectionwith the preceding figure. Therefore, further description is notbelieved to be necessary in connection with these features.

In this circuit modification, the supply of potentials for automaticvolume control purposes is obtained from a separate impedance element ina separate diode rectifier circuit provided in connection with thesecond rectifier anode 93 which, like the anode TI, is directlyassociated with the cathode I8 outside the electron stream of thetetrode.

High frequency or intermediate frequency signals are supplied to theanode 93 fromthe same circuit I6 as the anode I! through a couplingcondenser 99. The second diode rectifier circuit may be traced through alead 95 directly connected with the anode 93 and connected to the groundlead 89 through an impedance element or resistor 96, and a controlpotential supply resistor 9'! provided with a shunt radio frequencybypass condenser 98. The diode rectifier circuit is completed throughthe self bias resistor 99 and a cathode return lead 99 in which thisresistor is located. It should be noted that it is desirable to providea lower impedance at 99 than at 9'! in order that the major portion ofthe potential drop may occur in the resistor 91, and, therefore, beavailable-for control purposes.

It will be seen that with this arrangement. the potential existingacross the self bias resistor 99 is applied to the anode 93 inopposition to signal potentials impressed thereon by the circuit it,

whereby a delayed rectifier action is provided. This is for the reasonthat a positive potential is applied to the cathode 18 because of thepotential drop in the resistor 99, and a positive potential is alsoapplied to the anode 99 when rectification occurs on each positive halfcycle. Un til the positive signal potential on the anode 93 is greaterthan the positive potential existing on the cathode '58, norectification can take place.

Therefore, the delayed action on the rectifier anode 93 and a delayedautomatic volume control of the gain in the preceding amplifier devicesis obtained and, as is well known, is desirable in radio receivingsystems to permit a certain signal level to be reached beforesuppression of the gain is initiated.

Automatic volume control leads indicated at I90 are connected throughsuitable filter resistors indicated at I9I to the direct currentimpedance element 9'! for supplying controlling potentials to precedingamplifier devices, in the manner disclosed in Fig. 1. This connectionmay be made at any suitable point on the element 971 to provide thedesired potential for automatic volume control purposes, resulting fromrectification of the signal currents. Because 91 is of higher resistancethan 96, more D. C. voltage is developed across 91 for automaticvolumecontrol purposes, which is desirable in this case.-

It will be seen that in the embodiment of'the I fier circuit is providedwith an impedance elef- U ment in series with the diode-rectifiertherein to set up potentials whichin the audio frequency circuit mayvariably be applied to the control grid of the amplifier portion of thedevice I9, while in the case of the automatic volume control circuit,the impedance is utilized as a source of variable direct potentialswhich are responsive to the variations in intensity of the carrier waveto control the gain of preceding amplifier devices.

Referring now to Fig. 3, a similar circuit to that shown in Fig. 2 isillustrated, inwhich a pentode type electric discharge device I92, likethe device 28 of Fig. 1, is utilized in place of a tetrode. The cathodeis indicated at I49 and. the main anode at MI. The diode plate or anodeelectrodes associated with the cathode are shown at I42 and I43 and thescreen grid at I44. The cathode or suppressor grid is shown .at I45. Afixed tap connection I03 is provided on the-diode rectifier circuitimpedance 92a for applying to, the control grid indicated at I94,variable audio frequency potentials for further amplification- Theimpedance 82, with a condenser85, providesa suitable high frequencyfilter for the rectifier circuit.

The tap connection acoupling condenser I95 to one end of avolume controlpotentiometer resistor I96, theotherend of which is connecteddirectly-to the ground lead 89. The variable volume control tap I9! isconnected with a gridjleadIiIB which, in turn,

is connected with the low potential sideof the,

high frequency input circuit 12 and thence to, the

control grid I94. The lead I99 is provided with,

I93 is connected through an audio frequency coupling condenser I I whichmay be utilized instead of a transformer connection in certain receivingapparatus. Also, the coupling device I is untuned on the primary side asis desirable in certain receiving circuits.

The operation of the system shown in Fig. 3 is similar to that shown inFigs. 1 and 2. However, the arrangement has the advantage that the audiofrequency signals are applied to a potentiometer device lii6iil'|' whichis connected directly to ground at one end, whereby as the volume isreduced, the grid approaches or is finally connected to ground, therebyproviding a more stable operating circuit.

As the volume is increased, the maximum audio frequency signalpotentials are applied to the grid I04 when the tap I0! is at the upperend of the resistor I06, as viewed in the drawings. The potentialsavailable at that point are determined by the fixed tap I03 on thesignal ratio determining impedance element 82 in the rectifier circuit,the tap being placed at an intermediate point thereon for the purpose ofpreventing overload of the pentode-grid from audio frequency signalswhen the volume control device is at a maximum position.

It will be seen that the condenser I09 operates as a compensating tonecontrol, for the reason that the relative impedance between it and theimpedance of the potentiometer element I06 varies as the tap I0! ismoved along the latter, so that for very low volume adjustments of thetap I01, the shunt impedance of the condenser I09 is relatively highwith respect to the portion of the resistance I06" than in circuitbetween the tap and ground. Accordingly, the signal potentials in thehigher audio frequency range are less attenuated as the volume isreduced, which is desirable, as the human ear is less responsive to highfrequency sounds at low volume and the high frequency sounds are lessattenuated for low volume adjustment than at higher volume adjustmentsof the volume control device, whereby to the listening ear, the highfrequency sounds are maintained at substantially uniform relation to theremainder of the audio frequency range as the volume is reduced. Adesired compensated volume control and high frequency bypass arrangementis, therefore, provided in the circuit shown.

In order that the sensitivity of the preceding radio input circuit maybe controlled through a variation of the biasing potential applied tothe preceding amplifier devices in a receiving circuit such as thatshown in Fig. 1, the tap 81 on the automatic volume cohtrol supplyimpedance or resistor 88 may be made variable as indicated. Furthermore,this variable tap may be connected to or ganged with the volume controlpotentiometer I06 as indicated by the dotted connection I46 and may beprovided with a common operating 'means indicated at I41 whereby thesensitivity of the receiver may be reduced simultaneously with areduction in volume.

In the present example, movement of the potentiometer contact of thedevice I06 in a downward direction, as viewed in the drawings, causes areduction of the amplitude of audio frequency potentials applied to theinput grid J04. When ganged with the potentiometer orimpedance 83,simultaneous movement of the. contact 81 in the same direction isarranged as shown to cause an increase in the negative biasingpotentials supplied to the leads I00, thereby more effectively to biasthe preceding amplifier devices, such as those in Fig. 1, in a directionto reduce the gain therethrough.

With an arrangement as above described, an audio frequency volumecontrol potentiometer in the audio frequency rectifier circuit is gangedor connected with a sensitivity control potentiometer in the automaticvolume control potential supply circuit and arranged to be operated by acommon means simultaneously to control both the audio frequency signalgain through the audio frequency portion of the receiver and the highfrequency amplifier gain in the input portion of the receiver.

It Willbe noted that the automatic volume control diode lead I3 isreturned, in the circuit of Fig. 3, directly to the cathode lead 99,whereby no delayed automatic volume control action is provided. Thismay, however, be provided as in Fig.

2, by connection to the ground side of the self bias resistor 91.

A simplified and eflicient circuit for combined high frequencyamplification, diode signal and diode automatic volume controlrectification, audio frequency amplification and automatic volumecontrol operation is shown in Fig. 4, to which attention is nowdirected.

This circuit may utilize any suitable amplifierrectifier device. Ascreen grid tube or tetrode type as shown at I II is preferred, however,for a simplified circuit, and is provided with a high frequency inputcircuit I I2 connected with the control grid I I 3, a high frequencyoutput circuit H4 connected with the output anode H5 and with a couplingsystem IIG, to the high frequency lead I H of the diode input circuit towhich both diodes IIB-I I9 are connected in parallel, as in Fig. 1.

The diode circuit coupling device comprises a tuned high frequency chokecoil I 20' connected in the anode output circuit H4 in series with anaudio frequency output coupling resistor I2I provided with an audiofrequency output coupling condenser I22, thereby providing a similaroutput circuit to that shown in Fig. 3.

The high frequency choke coil I20 is connected through a high frequencycoupling condenser I 23, to a coupling impedance or choke coil I24, inthe diode rectifier circuit I I1, providing an input device therefor.The two choke coils I24 and I20 are electrically separated by a groundedshield I25, whereby electrostatic coupling only is provided between themthrough the condenser I23. The condenser preferably should have arelatively high impedance to audio frequency signals. This circuitarrangement provides a relatively high selection just preceding thediode rectifier or detector which is desirable for preventinginterference in certain radio receiving systems.

The diode rectifier circuit is completed from the cathode, indicated atI21, through a cathode lead i28 directly to the ground lead I29, andfrom the ground lead I29 through the rectifier circuit impedance I30which, in itself, provides the volume control potentiometer means, andfrom the opposite end of the potentiometer resistor I30 directly to thelow side I3I of the input device I24.

Audio frequency signals existing in the diode rectifier circuit andavailable across the impedance element I30 are controlled in amplitudeand applied to the inner or control grid II3 through a grid lead I32 andthehigh frequency input circuit II 2 by the variable tap I33 of thepotentiometer device. Movement of the tap I33 serves to control theaudio frequency volume as in the preceding embodiments of the invention.

R tential taken through the same contact.

Control potentials for automatic volume control purposes are alsoderived from the direct potential drop in the impedance element I30through a suitable connection thereon. In the present example thisconnection is made normally at the high potential point indicated atI34, and the potentials therefrom are conducted through a lead I toautomatic volume control leads I36, in which are located suitable filterresistors I31, and across which is connected a suitable bypass capacitor33, forming with the resistors I 3?, a filtei for the automatic volumecontrol leads.

In the embodiment of the invention shown in Fig. 3, the audio frequencyvolume control means and a sensitivity control means for a receivingsystem are shown in ganged relation. In the present embodiment of theinvention, the single potentiometer device H30 may be arranged incircuit to control both the audio frequency gain and the bias potentialsupply for preceding amplifier devices through the medium of aconnection with both the input lead I32 for the control grid H3 and theautomatic volume control bias supply leads I 36.

To this end, a suitable switch, such as a twoway switch I45, is arrangedto connect the input ends of the circuit leads I36 alternatively withthe potential supply lead I35 or with the lead I32.

In the present arrangement, the switch ,arm I539 is connected through alead I5!) with the input terminal ends of the filter resistors I31 andis arranged to connect with either of two contacts I5! or 52. Thecontacts are connected respectively with the leads I35 and I32, wherebythe D. C. component of the signal potential available across theresistor I 30 may be taken in full through the lead I35 or in part assupplied by the contact I33 through the lead I32.

The connection is normally made as indicated, to the lead I35. It willbe seen, however, that when connected to contact I52, the biasingpotential supplied to leads I36 may simultaneously be varied byoperation of the contact I32 along with the audio frequency component ofthe signal po- With this arrangement, combined audio frequency andsensitivity control is provided through a single instrumentality in theform of a simple potentiometer resistor.

It will be noted in connection with the circuit shown and describedherein, that the operating bias potential for the control grid II3 isderived wholly from the resistor or impedance element its and such biaspotentials result only from the reception of a signal and fromrectification thereof, so that the control grid is diode biased orsignal biased and the bias potential automatically increases withincreasing signal, and with increased output volume resulting therefrom'the adjustment of the volume control tap I33. This arrangement has theadvantage that the bias potential applied to the control gridautomatically increases with increased signal strength and with anincrease in the volume adjustment.

Thus, the system shown in Fig. 4 differs from that shown in thepreceding figures, wherein the biasing potentials are derived from afixed source such as a self bias resistor in the cathode return lead ofthe amplifier device.

From the foregoing description of the circuit shown in Fig. 4 it will beseen that through the medium of a single variable potentiometer deviceinserted as an impedance element in a rectifier circuit between a highfrequency amplifier input circuit and a low frequency output circuit, inconjunction with a combined amplifier and rectifier device having acommon cathode, combined high frequency amplification, rectified signaland automatic volume control potentials, audio frequency amplification,and simultaneous control of audio frequency and sensitivity control maybe obtained, the one potentiometer device serving as a source of bothvariable and fixed signal and direct current components of the rectifiedcurrent.

This circuit has the further advantage that the bias potential suppliedto all amplifiers, including theaudio frequency amplifier, is increasedautomatically with increase in the signal strength along with the signalpotential applied to the audio frequency amplifier, and that'no fixedadditional source of bias potential is required, thereby simplifying theproblem of supplying biasing potentials for the amplifier devices.

This circuit arrangement results in a simplificaticn of the receivingsystem, a reduction in the number of circuit elements required, andconsequently a reduction in the'cost of manufacture of apparatusembodying this circuit.

The use of a single electric discharge device for four major functions,including the control of biasing and signal potentials by a single meansin a receiving circuit, is of considerable importance in apparatus suchas automobile and other battery operated portable receivers where thesize of the complete apparatus, the current consumption and cost of saidapparatus must necessarily be kept at a minimum.

I claim as my invention:

. 1. In a radio signal receiving system, the com-' bination with anelectric discharge device having a cathode, an anode electrodeassociated therewith to provide a rectifier, a control grid and a mainoutput anode, of a signal input circuit connected with said controlgrid, a rectifier circuit for said rectifier connected with said mainoutput anode to receive the signal output therefrom, an impedancenetwork providing coupling means between the rectifier-circuit and saidinput circuit, said network including a fixed and a variable impedanceelement providing a fixed and a variable potential drop determiningmeans in said etwork, said variable potential drop determining meanscomprising a potentiometerhaving a resistor element and a movable tapthereon, one end of said resistor being connected with the cathode andsaid movable tap being connected with the fixed impedance element, andmeans. connected between the other end of the resistor element and thecontrol grid for applying signal potentials to said grid.

2-. In a radio signal receiving system, the combination with an electricdischarge device having a cathode, an anode electrodeassociatedtherewith to provide a rectifier, a control grid and a main outputanode,of a signal input circuit con-s nected with saidcontrol grid, a signaloutput circuit connected with the main output anode, a rectifier circuitfor said rectifier connected with said main output anode, and animpedance net work providing a coupling means between the rectifiercircuit and said input circuit, said network including a fixed and avariable impedance element providing fixed and variable potential. dropdetermining means in said network, said variable impedance element beingconnected between the cathode and said control grid and havin a movabletap connection with said fixed impedance element.

3. In a signal receiving system, the combination of an electricdischarge device comprising amplifier and rectifier elements having acommon cathode in a single envelope, a signal input circuit and a signaloutput circuit for said amplifier element, a variable volume controlimpedance device in circuit with said rectifier element connected withsaid input circuit to variably apply rectified signals thereto, a secondvariable impedance device, circuit means for supplying rectified currenttherethrough from said rectifier element, an amplifier control circuitconnected with said second variable impedance device to receivecontrolling potentials therefrom, means for simultaneously controllingsaid variable impedance elements, means for coupling said output circuitto said rectifier element, and means for receiving signals from saidoutput circuit.

i, In a radio signal receiving system, the combination with an electricdischarge device having a cathode, an anode electrode associatedtherewith to provide a rectifier, a control grid and a main outputanode, of a signal input circuit connected with the rectifier anode andwith the cathode, an impedance element in the last-named connection,means for variably connecting the control grid with said impedanceelement to supply rectified signal and biasing potentials to said gridfrom said impedance element, said potentials being therebysimultaneously variable, and an amplifier circuit connected with saidimpedance element to receive gain controlling potentials therefromsimultaneously variable with said first named potentials.

5. In a signal receiving system, the combination of an electricdischarge device comprising amplifier and rectifier elements having acommon cathode in a single envelope, signal input and output circuitsfor said amplifier element, a circuit for controlling the sensitivity ofsaid system, and means for simultaneously varying the control potentialsapplied to said last named circuit and signal potentials applied to saidamplifier element, said means including a variable potentiometer devicein circuit with the rectifier element and connected with the signaloutput circuit.

6. In a radio signal receiving system, the combination with an electricdischarge device having a cathode, an anode electrode associatedtherewith to provide a rectifier, a control grid and a main outputanode, of a signal input circuit connected with said rectifier, animpedance network including a variable impedance element, connected inpart in circuit with said rectifier and in part between said rectifiercircuit and the control grid, whereby said control grid is coupled tosaid rectifier to receive signals therefrom, the connection with thecontrol grid being direct with said impedance element whereby directbiasing potentials may be received therefrom, a sensitivity controlcircuit for said system, and means for connecting said circuit with saidvariable impedance element, whereby control potentials simultaneouslyvariable with said biasing potentials may be applied to said controlcircuit.

'7. In a radio signal receiving system, the combination with an electricdischarge device having a cathode, an anode electrode associatedtherewith to provide a rectifier, a control grid and a main outputanode, of an impedance network including a variable impedance element,connected between the control grid and the rectifier, and a fixedvoltage ratio determining impedance element in circuit with saidvariable impedance element.

8. In a radio signal receiving system, the combination with an electricdischarge device having a cathode, an anode electrode associatedtherewith to provide a rectifier, a control grid and a main outputanode, of an impedance network including a variable impedance element,connected between the control grid and the rectifier, a fixed voltageratio determining impedance element in circuit with said variableimpedance ele-- ment, and means associated therewith in circuit toprovide a filter.

9. In a radio signal receiving system, the combination with an electricdischarge device having a cathode, a pair of anode electrodes associatedtherewith, a control g 'id and a main output anode, of an impedancenetwork including a variable impedance element connected between thecontrol grid and the cathode, a rectifier circuit connected between onerectifier anode element and the cathode through said impedance element,a second rectifier circuit, a second impedance element in said secondrectifier circuit with the other rectifier anode electrode, and acontrol circuit connected with said last-named impedance element toreceive a direct current controlling potential therefrom.

10. In a signaling system, an electric discharge amplifier device havinga cathode and at least one rectifier plate associated therewith toprovidea rectifier, of a signal input circuit for said device, a signaloutput circuit for said device, high and low frequency impedance meansin said output circuit, a signal circuit connected with the lowfrequency impedance means, a rectifier circuit, including the cathodeand one rectifier plat-e, connected with said high frequency impedancemeans, impedance means connected in circuit between the cathode and thesignal input circuit, a second impedance means connected in saidrectifier circuit, means for deriving a potential from said secondimpedance means, and for applying a derived potential variably to saidfirst impedance means.

11. In a radio signal transmission circuit, a diode rectifier and anelectrical impedance device connected in series therewith, means forsupplying high frequency signal potentials to said rectifier, anelectronic tube amplifier having a cathode providing one electrode ofsaid rectifier and a control grid connected with said impedance device,a variable impedance network providing said connection, means providinga low frequency separate output circuit for said amplifier, a seconddiode rectifier having an anode electrode associated with said cathode,circuit means for applying signals to said anode, a low impedance devicein circuit adjacent to said anode, and a high impedance device incircuit adjacent to said cathode in series in circuit with said secondrectifier circuit, and a control circuit connected with said last-namedimpedance device to receive direct-current controlling potentialstherefrom.

12. In a radio receiving system, the combination with an electricdischarge amplifier device having in a common envelope, a cathode, aconan impedance element, means providing a connection between saidimpedance element and. the

ico'ntr'ol grid, and a low frequency output circuit connected with saidfirst-named anode.

tion with an electric discharge amplifier and rectifier devicecomprising a cathode, a control electrode, an anode, and at least oneauxiliary anode associated with the cathode, of a signal input circuitfor said control electrode including a high frequency impedance element,a low frequency impedance element, an output circuit for the first-namedanode including a second high frequency impedance element and a secondlow frequency impedance element, a rectified circuit including saidauxiliary anode and the cathode connected with the output circuitthrough the second named high frequency impedance element, andpotentiometer means providing a variable connection between saidrectifier circuit and the signal input circuit between the highfrequency impedance element and the low frequency impedance elementtherein.

14. In a radio receiving system, the combination with an electricdischarge amplifier and rectifier device comprising a cathode, a controlgrid, an anode, and at least one auxiliary anode associated with thecathode, a signal input circuit for said control grid including a highfrequency a rectifier circuit including the auxiliary anode and thecathode connected with the output anode circuit through the second highfrequency impedance element, means providing potential drop producingresistance and a variable potentiometer connection between saidrectifier circuit and the input circuit, a high frequency amplifierconnected with the first named input circuit, said amplifier having anautomatic gain control circuit, and means providing a connection for thelast-named circuit with said potential drop producing means forreceiving automatic gain controlling potentials therefrom established bya direct current component of the signal current in said rectifiercircuit.

15. In a radio receiving system, the combination with an electricdischarge amplifier and rectifier device comprising a cathode, a controlgrid, an anode, and at least one auxiliary anode associated with thecathode, of a signal input circuit for said control grid including ahigh frequency impedance element, a low frequency impedance element anda source of biasing potential, an output circuit for the anode includinga second high frequency impedance element and a second low frequencyimpedance element, a rectifier circuit including the auxiliary anode andthe cathode connected with the output anode circuit through the secondhigh frequency impedance element, and means providing potential dropproducing resistance in the rectifier circuit and a variablepotentiometer connection between said rectifier circuit and a point onsaid input circuit between the high frequency impedance element and thelow frequency impedance element therein, and said rectifier circuitfurther including said source of biasing potential so poled that apredetermined fixed positive potential is applied to the cathode withrespect to the auxiliary anode in the rectifier circuit, whereby adelayed rectifier action is provided.

16. In a radio receiving system, the combination with an electricdischarge amplifier and rectifier device comprising a cathode, a controlgrid, an anode, and at least one auxiliary anode associated with thecathode, a signal input circuit for said control grid including a highfrequency impedance element, an output circuit for the anode, arectifier circuit includingthe auxiliary anode and the cathode connectedwith said outi put anode circuit, potential drop producing impedancemeans in said rectifier circuit, a common circuit lead connecting theinput and'output circuits with the cathode, and a potentiometer resistorconnected between a point on said potential drop producing impedance andsaid common circuit lead, and havingia variable contact connected withthe control grid.

17. In a radio receiving system, the combina-' tion with an electricdischarge amplifier and rectifier device comprising a cathode, a controlgrid, an anode, and at least one auxiliary anode associated with-thecathode, a signal input circuit for said control grid including a highfrequency impedance element, an output circuit for the anode, arectifier circuit including the auxiliary anode and the cathodeconnection with said output anode circuit, potential drop producingimpedance means in said rectifier circuit, a common circuit leadconnecting the input and output circuits with the cathode,apotentiometer resister connected between a point on said potential dropproducing impedance and said common circuit lead, and having a variablecontact connected with the control grid, and high frequency by-passmeans connected between the movable contact of said potentiometer andsaid common circuit lead.

18. In a radio receiving system, the combination with an electricdischarge device having a cathode, a control grid, an anode, and twoauxiliary anodes associated with the cathode, of a high frequencysignal-input circuit having one terminal connected to the control gridand having one terminal connected to the cathode through a potentiometerresistor, a rectifier circuit including said auxiliary anodes and thecathode and said potentiometer resistor, means for supplying amplifiedhigh frequency signals to said rectifier circuit whereby said controlgrid receives direct current potentials for biasing purposes andrectified signal potentials, from said potentiometer resistor, an audiofrequency output circuit connected with said anode, and a gain controlcircuit connected with said potentiometer device to receivedirect-current controlling potentials therefrom.

19. In a superheterodyne radio receiver for cult, means for variablyapplying a controlling potential from said impedance means to saidamplifier device through said input circuit, an automatic volume controlcircuit, and means for deriving a second controlling potential from saidimpedance means for said automatic volume control circuit.

20. In a signalling system, the combination with an electric dischargeamplifier and rectifier device having a control electrode, a cathode, anoutput anode, and at least one diode rectifier anode associated with thecathode, of a rectifier circuit connected between said rectifier anodeand the cathode and including a resistor provided with a movable tap, ahigh frequency signal input circuit connected between said controlelectrode and the movable tap on said resistor, high frequency couplingmeans connected between said output anode and the rectifier circuit, an

automatic volume control circuit connected with said resistor to receivecontrolling potentials therefrom, and a separate low frequency outputcircuit connected with said output anode in series with said highfrequency coupling means.

21. In a radio receiving system, a multi-electrode space current deviceand circuit connections whereby said device functions simultaneously toprovide volume control potentials, as a demodulator of incoming signalsand as an amplifier of the incoming signals as well as the demodulatedsignals, said device having electronic amplifier elements and electronicrectifier elements provided with a common cathode, and said circuitconnections including signal input and output circuits for saidamplifier elements, means for coupling said output circuit to saidrectifier elements, an impedance device in circuit with said rectifierelements for producing a potential drop corresponding to the amplitudeof received signals and the modulation component thereof, and automaticvolume control circuit variably connected with said impedance element,and means for selecting from said impedance element and applying to saidamplifier elements a demodulated signal.

22. In a radio signal receiving system, the combination with an electricdischarge device having a cathode, an anode electrode associatedtherewith to provide a rectifier, a control grid and a main outputanode, of a signal input circuit connected with said control grid, arectifier circuit for said rectifier connected with said main outputanode to receive the signal output therefrom, and an impedance networkproviding coupling means between the rectifier circuit and said inputcircuit, said network including a fixed tapped voltage divider resistorproviding a tap connection for said input circuit, means for applyingsignal potentials across the terminals of said voltage divider resistorand a potentiometer resistor in circuit with said voltage dividerresistor for varying the potentials derived therefrom for said inputcircuit.

23. In a radio signal receiving system, the combination with an electricdischarge device having a cathode, an anode electrode associatedtherewith to provide a rectifier, a control grid and a main outputanode, of a signal input circuit connected with said control grid, arectifier circuit for said rectifier connected with said main outputanode to receive the signal output therefrom, an impedance networkproviding coupling means between the rectifier circuit and said inputcircuit, said network including a fixed and a variable impedance elementproviding a fixed and a Variable potential drop determining means insaid network, a self bias resistor in circuit With the cathode, meansfor utilizing the potential drop in said resistor to provide a delaypotential for said rectifier, and means for utilizing potentials derivedfrom said rectifier above a predetermined delay potential for automaticvolume control of said system.

ROGERS M. SMITH.

